Method for manufacturing concentric double exhaust pipe for internal combustion engine

ABSTRACT

A concentric double exhaust pipe for an internal combustion engine includes an outer pipe  10  and an inner pipe  20.  The outer pipe  10  and inner pipe  20  have basal ends fixed to each other. A seal member  30  arranged between the two pipes  10  and  20  enable sliding of distal ends of the outer pipe  10  and the inner pipe  20  during thermal expansion. When manufacturing the concentric double exhaust pipe, the outer pipe  10  is compressed after attaching the seal member  30  between an inner surface of the outer pipe  10  and an outer surface of the inner pipe  20  so as to compress the seal member  30  to a predetermined outer diameter.

BACKGROUND OF THE INVENTION

The present invention relates to a method for manufacturing a concentric double exhaust pipe for an internal combustion engine.

Japanese Laid-Open Patent Publication No. 6-336921 describes a concentric double exhaust pipe, which is formed by arranging an inner pipe inside an outer pipe, used as an exhaust passage for an internal combustion engine. In the concentric double exhaust pipe, the two pipes have basal ends that are fixed to each other through welding or the like and distal ends that are free to tolerate thermal deformation in the axial direction of the pipes. More specifically, as shown in FIG. 3, after fixing the basal ends, which are not shown in the drawings, of an outer pipe 1 and an inner pipe 20 to each other, a wire mesh 3 is attached in a compressed state between the inner surface of the outer pipe 1 and the outer surface of the inner pipe 20 at the distal ends. This fixes the basal ends of the outer pipe 1 and inner pipe 20 and seals the distal ends of the outer pipe 1 and inner pipe 20 in a manner enabling sliding therebetween when thermal expansion occurs.

Normally, dimensional tolerance is provided for the inner diameter of the outer pipe 1 and the outer diameter of the inner pipe 20. This produces differences in the gap between the inner surface of the outer pipe 1 and the outer surface of the inner pipe 20. Therefore, if the gap between the inner surface of the outer pipe 1 and the outer surface of the inner pipe 20 is larger than the specified value for the thickness of wire mesh 3, the compression level of the wire mesh becomes too small. This causes the contact pressure of the wire mesh 3 against the outer pipe 1 and the inner pipe 20 to be less than the designed value. On the other hand, if the gap between the inner surface of the outer pipe 1 and the outer surface of the inner pipe 20 is smaller than the specified value for the thickness of the wire mesh 3, the compression level of the wire mesh becomes too high. This causes the contact pressure of the wire mesh 3 against the outer pipe 1 and the inner pipe 20 to be greater than the designed value. Further, when the gap is too small in relation with thickness of the wire mesh 3, the wire mesh 3 may become crimped. As a result, the sliding and sealing characteristics may not be satisfactory.

Such a problem occurs when manufacturing a concentric double exhaust pipes for an internal combustion engine enabling sliding during thermal expansion of the distal ends of the outer pipe and inner pipe by fixing the basal ends of the outer pipe and inner pipe and attaching a seal member between the inner surface of the outer pipe and the outer surface of the inner pipe.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a manufacturing method for a concentric double exhaust pipe for an internal combustion engine that facilitates attachment of a seal member between an outer pipe and an inner pipe and facilitates control of contact pressure of a seal member against an outer pipe and an inner pipe.

One aspect of the present invention is a concentric double exhaust pipe for an internal combustion engine including an outer pipe and inner pipe having basal ends fixed to each other. A seal member is arranged between the outer pipe and the inner pipe and enables relative movement of distal ends of the outer pipe and the inner pipe during thermal expansion. A method for manufacturing the concentric double exhaust pipe includes compressing the outer pipe after attaching the seal member between an inner surface of the outer pipe and an outer surface of the inner pipe so as to compress the seal member to a predetermined outer diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram of a concentric double exhaust pipe according to a preferred embodiment of the present invention prior to compression;

FIG. 2 is a cross-sectional diagram of the concentric double exhaust pipe subsequent to compression; and

FIG. 3 is a cross-sectional diagram of a concentric double exhaust pipe in the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A process for manufacturing a catalytic converter arranged in an exhaust passage of an internal combustion engine according to a preferred embodiment of the present invention will now be described with reference to FIGS. 1 and 2.

FIG. 1 is a cross-sectional diagram of a concentric double exhaust pipe for the catalytic converter showing a state prior to compression.

As shown in FIG. 1, the concentric double exhaust pipe of the catalytic converter includes an outer pipe 10, an inner pipe 20, and a wire mesh 30. The outer pipe 10 is formed from a steel metal. The outer pipe 10 has an outer diameter and an inner diameter, which are constant.

The inner pipe 20 includes a constant diameter portion 22, an enlarged diameter portion 24, and an end portion 24 e. The constant diameter portion 22 is concentric with the outer pipe 10. The outer diameter and inner diameter of the inner pipe 20 are each constant along the constant diameter portion 22. The enlarged diameter portion 24 has an end located at the upstream side of the exhaust and is welded to the outer surface of the constant diameter portion 22. The outer diameter and inner diameter of the inner pipe 20 at the enlarged diameter portion 24 gradually increases in the downstream direction of the exhaust. The end portion 24 e is located at the downstream side of the enlarged diameter portion. The outer diameter and inner diameter of the inner pipe 20 at the end portion 24 e are each constant.

The outer pipe 10 and the inner pipe 20 have basal portions at the upstream side of the exhaust that are welded to a fastening portion, which is not shown in the drawing. A wire mesh 30, which functions as a seal member, is arranged between the inner surface of the outer pipe 10 and the outer surface of the end portion 24 e of the inner pipe 20. The wire mesh 30 is formed from fine metal wires. The wire mesh 30 seals the gap between the inner surface of the outer pipe 10 and the outer surface of the end portion 24 e of the inner pipe 20. Further, the wire mesh 30 enables sliding of the two pipes 10 and 20 in the axial direction when the outer pipe 10 and the inner pipe 20 thermally deform.

With reference to FIGS. 1 and 2, the manufacturing procedures for the concentric double exhaust pipe when the wire mesh 30, which is attached to the end portion 24 e of the inner pipe 20, has a diameter d3 o smaller than an inner diameter d1 i of the outer pipe 10, that is, when a gap exists between the inner surface of the outer pipe 10 and the outer surface of the wire mesh 30 will now be discussed.

The concentric double exhaust pipe is manufactured in the following order from (1) to (10).

(1) As shown in FIG. 1, the basal portion at the exhaust upstream side of the enlarged diameter portion 24 is welded and connected to the distal portion at the exhaust downstream side of the constant diameter portion 22 to assemble the inner pipe 20.

(2) The outer pipe 10 is arranged concentrically with the inner pipe 20, and the basal portions at the exhaust upstream side of the outer pipe 10 and the inner pipe 20 are respectively welded to the fastening portion (not shown).

(3) The inner diameter d1 i and outer diameter d1 o of the outer pipe 10 are each measured at a section corresponding to the attachment position of the wire mesh 30. Then, the thickness Δd1 of the outer pipe 10 is calculated from the measured inner diameter d1 i and the outer diameter d1 o.

(4) The outer diameter d2 o of the end portion 24 e is measured.

(5) The wire mesh 30 is widened in the radial direction and attached to the outer surface of the end portion 24 e.

(6) The outer diameter d3 o of the wire mesh 30 in a state attached to the end portion 24 e is measured.

(7) The thickness Δd3 of the wire mesh 30 is calculated from the outer diameter d3 o of the wire mesh 30 and the outer diameter d2 o of the end portion 24 e.

(8) A target thickness Δd3 t, which is a compression target for the wire mesh 30, is calculated from the thickness Δd3 of the wire mesh 30.

(9) A target outer diameter d1 ot, which is a compression target for the outer pipe 10, is calculated from the outer diameter d1 o and thickness Δd1 of the outer pipe 10 and thickness Δd3 and target thickness Δd3 t of the wire mesh 30.

(10) As shown in FIG. 2, a spinning process is performed to compress the outer pipe 10 until the outer diameter d1 o of the outer pipe 10 becomes equal to the target outer diameter d1 ot. More specifically, a mold (not shown) is fixed to the end portion 24 e of the inner pipe 20. In this state, a roller (not shown) is pressed against the outer surface of the outer pipe 10 while rotating the outer pipe 10 together with the inner pipe 20. Further, the moving velocity of the roller in the axial direction and the feed amount of the roller in the radial direction are adjusted. The roller is pressed against the outer surface of the outer pipe 10 to compress the outer pipe 10 and the wire mesh 30 until the outer diameter d1 o of the outer pipe 10 becomes equal to the outer pipe target outer diameter d1 ot.

The preferred embodiment has the advantages described below.

(1) In the preferred embodiment, after the wire mesh 30 is attached between the inner surface of the outer pipe 10 and the outer surface of the inner pipe 20, the outer pipe 10 is compressed so as to compress the wire mesh 30 to the predetermined outer diameter. In this case, during the attachment of the wire mesh 30, the gap between the inner surface of the outer pipe 10 and the outer surface of the inner pipe 20 may be enlarged. This facilitates the attachment of the wire mesh 30 between the inner surface of the outer pipe 10 and the outer surface of the inner pipe 20. Further, the compression of the outer pipe 10 absorbs the dimensional tolerances of the outer pipe 10, the inner pipe 20, and the wire mesh 30. This facilitates control of the contact pressure of the wire mesh 30 against the outer pipe 10 and the inner pipe 20.

(2) The spinning process compresses the outer pipe 10. The spinning process is optimal for processes that require a high dimensional accuracy. The compression of the outer pipe 10 through spinning finely adjusts the compression level of the wire mesh 30. Thus, the sliding and sealing characteristics obtained by the wire mesh 30 may be finely controlled.

(3) The thickness Δd3 of the wire mesh 30 when attached to the end portion 24 e of the inner pipe 20 is measured, and the compression level of the outer pipe 10 is adjusted based on the measurement result. In this case, the compression force applied to the wire mesh 30 by the outer pipe 10 is accurately adjusted. Thus, the sliding and sealing characteristics obtained by the wire mesh 30 are improved.

(4) Due to the requirement for high heat resistance, the wire mesh 30 is often used as a seal member in a concentric double exhaust pipe for an internal combustion engine. However, the elasticity of the wire mesh 30 is not that high. It is thus difficult to adjust the contact pressure of the wire mesh 30 against the outer pipe 10 and the inner pipe 20 to a predetermined value. Further, the wire mesh 30 may be crimped when the wire mesh 30 is attached between the outer pipe 10 and the inner pipe 20.

In the preferred embodiment, even if the wire mesh 30, which is formed from fine metal wires, is used as the seal member, the arrangement of the seal member in the gap between the outer pipe 10 and the inner pipe 20 is facilitated. Further, the contact pressure of the seal member against the outer pipe 10 and the inner pipe 20 is controlled to a predetermined value.

The above embodiment may be modified as described below.

In the preferred embodiment, the wire mesh 30 is used as the seal member. However, a seal member formed from, for example, a heat resistant resin may also be used.

In the preferred embodiment, the measurement of the outer diameter d1 o and the inner diameter d1 i of the outer pipe 10 may be eliminated. Further, the measurement of the outer diameter d3 o of the wire mesh 30 and the outer diameter d2 o of the inner pipe 20 may be eliminated. This would lower the accuracy of the compression level of the outer pipe 10 and the wire mesh 30. However, the attachment of the wire mesh 30 would be facilitated, and the dimensional tolerances of the outer pipe 10, the inner pipe 20, and the wire mesh 30 would be absorbed.

In the preferred embodiment, the spinning process for compressing the outer pipe 10 and the wire mesh 30 may be changed to other processes, such as a pressing process.

The present invention is embodied in a catalytic converter for eliminating harmful substances from exhaust gas. However, the present invention may be embodied in a muffler that is arranged in an exhaust passage. In other words, the present invention may be applied to any concentric double exhaust pipe having an outer pipe and inner pipe with fixed basal ends and distal ends allowed to slide.

In the preferred embodiment, instead of compressing the outer pipe 10 after attaching the wire mesh 30 between the inner surface of the outer pipe 10 and the outer surface of the inner pipe 20, the inner pipe 20 may undergo a diameter enlargement process to compress the wire mesh 30. Such processing would be more difficult than the compression of the outer pipe 10. However, this would facilitate the attachment of the wire mesh 30 and absorb the dimensional tolerances of the outer pipe 10, the inner pipe 20, and the wire mesh 30. Further, the contact pressure of the wire mesh 30 against the outer pipe 10 and the inner pipe 20 may be controlled. 

1. A method for manufacturing a concentric double exhaust pipe for an internal combustion engine, the exhaust pipe including an outer pipe and inner pipe having basal ends fixed to each other, with the inner pipe arranged in the outer pipe, and a seal member arranged between the outer pipe and the inner pipe and enabling relative movement of distal ends of the outer pipe and the inner pipe during thermal expansion, the method comprising: compressing the outer pipe after attaching the seal member between an inner surface of the outer pipe and an outer surface of the inner pipe so as to compress the seal member to a predetermined outer diameter.
 2. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 1, wherein the outer pipe is compressed through a spinning process.
 3. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 1, wherein the outer pipe is compressed through a pressing process.
 4. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 1, further comprising: measuring thickness of the seal member when attached to the outer surface of the inner pipe and adjusting compression level of the outer pipe based on the measurement.
 5. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 4, further comprising: calculating a target diameter, which is a compression target for the outer pipe, based on the outer diameter and thickness of the outer pipe and a target thickness, which is a compression target, for the seal member.
 6. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 1, wherein the seal member has an outer diameter measured when attached to the outer surface of the inner pipe that is set to be smaller than an inner diameter of the outer pipe.
 7. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 1, wherein the seal member is attached to the outer surface of the inner pipe in a state in which the seal member is widened in the radial direction.
 8. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 1, further comprising: fixing a mold inside the inner pipe and pressing a roller against an outer surface of the outer pipe while rotating the outer pipe together with the inner pipe.
 9. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 8, further comprising: adjusting moving velocity of the roller in the axial direction of the outer pipe and feed amount of the roller in the radial direction of the outer pipe to compress the outer pipe.
 10. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 1, wherein the seal member is a wire mesh formed from fine metal wires.
 11. The method for manufacturing a concentric double exhaust pipe for an internal combustion engine according to claim 1, wherein the outer pipe is formed from a steel metal.
 12. A method for manufacturing a concentric double exhaust pipe for an internal combustion engine, the exhaust pipe including an outer pipe and inner pipe having basal ends fixed to each other, with the inner pipe arranged in the outer pipe, and a seal member arranged between the outer pipe and the inner pipe and enabling relative movement of distal ends of the outer pipe and the inner pipe during thermal expansion, the method comprising: performing a diameter enlargement process on the inner pipe after attaching the seal member between an inner surface of the outer pipe and an outer surface of the inner pipe so as to compress the seal member to a predetermined outer diameter. 